Balaji Mohan

Cavitation in Injector Nozzle Holes – A Parametric Study

Abstract The fuel injection system in diesel engines has a consequential effect on the fuel consumption, combustion process and formation of emissions. Cavitation and turbulence inside a diesel injector play a critical role in primary spray breakup and development processes. Thus understanding the phenomenon of cavitation is significant in capturing the injection process with accuracy. In this study, the cavitating flow inside an injector nozzle hole was numerically investigated. The two-phase mixture model by Schnerr and Sauer (2001) was adopted along with k-ε turbulence model and Fluent CFD package was used to solve the governing equations numerically. The validation of the model was done by comparing the numerical results with the experimental results of Winklhofer et al. (2001) for U-throttle geometry and a good agreement was found. In this paper, a detailed parametric study on the effects of injection pressure, transient analysis for diesel and SME (Soy Methyl Esther) bio-diesel and different geometries on cavitation phenomenon inside the injector nozzle hole was done. The results show that the bio-diesel inhibits the cavitation phenomenon compared to diesel fuel, and positive Kfactor nozzles have higher mass flow rate and higher exit velocity.

Molecular dynamics simulation of gas-phase ozone reactions with sabinene and benzene

Gas-phase reactions of ozone (O3) with volatile organic compounds were investigated both by experiment and molecular simulations. From our experiments, it was found ozone readily reacts with VOC pure components and reduces it effectively. By introducing ozone intermittently, the reaction between VOC and ozone is markedly enhanced. In order to understand the relationship between intermediate reactions and end products, ozone reaction with benzene and alicyclic monoterpene sabinene were simulated via a novel hybrid quantum mechanical/molecular mechanics (QM/MM) algorithm that forced repeated bimolecular collisions. Molecular orbital (MO) rearrangements (manifested as bond dissociation or formation), resulting from the collisions, were computed by semi-empirical unrestricted Hartree-Fock methods (e.g., RM1). A minimum of 975 collisions between ozone and targeted organic species were performed to generate a distribution of reaction products. Results indicated that benzene and sabinene reacted with ozone to produce a range of stable products and intermediates, including carbocations, ring-scission products, as well as peroxy (HO2 and HO3) and hydroxyl (OH) radicals. Among the stable sabinene products observed included formaldehyde and sabina-ketone, which have been experimentally demonstrated in gas-phase ozonation reactions. Among the benzene ozonation products detected composed of oxygen mono-substituted aromatic C6H5O, which may undergo further transformation or rearrangement to phenol, benzene oxide or 2,4-cyclohexadienone; a phenomenon which has been experimentally observed in vapor-phase photocatalytic ozonation reactions.